Apollo 6: Saturn V's Shaky Dress Rehearsal

Apollo's lunar missions were not launched from Cape Kennedy.
Launch Complex 39, where Saturn Vs were launched, was on Kennedy Space
Center grounds. (Launch Complexes 34 and 37 were on the Air Force
Eastern Test Range, on the Cape itself.) Of the three launch areas
planned for Complex 39 and shown in the 1965 drawing (the three
right-hand areas above), the one at the extreme right, Area C, was not
constructed; Areas (or Pads) A and B were built and used for all Saturn
V launches.

The success of Apollo 4 gave good reason to believe that
the Saturn V could be trusted to propel men into space. But NASA pushed
on with its plans for a second unmanned booster flight, primarily to
give the Pad 39 launch team another rehearsal before sending men into
deep space on the Saturn V.

Getting Apollo 6 to the launch pad was a lengthy process. The S-IC first
stage of the Saturn V arrived at Kennedy Space Center* on 13 March 1967. Four days later it was on
a mobile launcher in the cavernous assembly building, awaiting the S-II
second stage - which did not get to Kennedy until May. On 6 February
1968, a Tuesday morning, a crawler carrying the whole Apollo stack on
its platform edged out of the building into a wind-driven rain and
headed slowly down a track to the launch complex, five kilometers away.
En route, trouble with communications circuits forced a two-hour wait.
When communications were restored, the crawler resumed its snail's pace.
At 5:00 that afternoon, the rain stopped, and the Apollo stack arrived
at the launch area an hour later.33

Although the spacecraft itself had no primary objectives to accomplish,
a Block I version (CSM-020) with many Block II improvements (such as the
new hatch) was allocated to the mission. Kleinknecht, the command and
service modules manager in Houston, was pleased with the machine that
North American sent to Kennedy, although he was upset when he learned
that the protective Mylar film that covered the spacecraft during
shipment was flammable. In engineering terms, it was a clean spacecraft.
Only 23 engineering orders were outstanding (as opposed to the hundreds
listed for spacecraft 012 only a year and a half earlier), and most of
these were the kind that the spacecraft operations people at Kennedy
normally handled anyway.34 The
spacecraft had no last-minute problems, but the mission planners did.

In November 1967, the idea of putting a camera in the window of the
spacecraft to take some earth resources photographs had been explored in
a review for Mueller at North American. John Mayer's MSC mission
planners were hit hard by the late inclusion of the camera. Because
Apollo 6 was unmanned, all the flight trajectory data had to be
correlated with the photographic aims and a computer program had to be
developed and fed into the onboard computer. After many careful checks,
the mission planners decided that there might be a chance during the
first orbit and part of the second to get some pictures of the area from
Baja California to Texas.35

Apollo 6 had been scheduled for the first quarter of 1968, but several
brief postponements slipped it past that date. On 15 January, Mueller
wrote Webb that the tank skirt of service module 008 had split during
structural testing. The skirt on spacecraft 020 was strengthened to
prevent a similar mishap. Then, after the stack had been trundled down
the path to the launch area on a rainy day, water seepage was found in
the Saturn's S-II stage, and some parts had to be replaced. And,
finally, the countdown-to-launch practice did not end until 29 March.36

At 7:00 a.m. on 4 April 1968, Saturn V 502 rose thunderously from its
Florida launch pad to boost Apollo 6 (AS-502) into orbit,
but that was nearly the last normal thing the big rocket did. For the
first two minutes, the five huge engines in the first stage roared,
shook the ground, and belched fire evenly. Then there were thrust
fluctuations that caused the vehicle to bounce like a giant pogo stick
for about 30 seconds. Low-frequency modulations (known as the pogo
effect) as high as +/-0.6 g were recorded in the command module, which
exceeded design criteria (0.25 g was the upper limit permitted for
manned flight in Gemini). Except for the bouncing and the loss of a
piece of the panel in the adapter, the first stage did its job,
however.

Very shortly after the second stage ignited, two of its five J-2 engines
stopped. The other three engines had to fire longer to compensate for
this loss of power. The second stage did not reach the desired altitude
and velocity before its fuel gave out and it dropped away. To reach the
required speed, the S-IVB third stage also had to burn longer than
planned, putting the spacecraft into an orbit of 178 by 367 kilometers,
instead of a 160-kilometer circular orbit.

Mission Director Schneider and Flight Director Clifford E. Charlesworth
left the vehicles in a parking orbit for two circuits of the earth while
system checks were performed, operational tests were conducted, and
several attitude maneuvers were carried out. Then flight control tried
to restart the S-IVB, to simulate translunar injection, but the third
stage refused to answer the call. The next step was to separate the
command and service modules from the now useless S-IVB.

While Apollo 6 had been whirling around the earth, the
spacecraft's special 70-millimeter camera had been clicking away,
getting some spectacular color stereo photographs.** These were later found to be excellent for
cartographic, topographic, and geographic studies of continental areas,
coastal regions, and shallow waters.

Mouth of the Colorado River and Gulf of California were
photographed from the Apollo 6 spacecraft 220 kilometers above
on 4 April 1968. Baja California is at the left, and the Mexican state
of Sonora, showing the Sonoran Desert, is to the right of the river's
mouth.

Following the system checks and the photography, controllers turned to
an alternate mission. The service module engine was fired for 442
seconds,*** which exceeded lunar
mission requirements, to produce the simulated translunar injection
maneuver. Apollo 6 shot out to 22,200 kilometers. Although
the spacecraft had enough altitude for a good simulation of an Apollo
spacecraft returning to the earth from the moon, the service module
engine no longer had sufficient fuel to give it the correct speed for
its dive. The command module reached a velocity of 10,000 meters per
second, about 1,270 less than planned, and splashed down in the Pacific,
missing its predicted impact point by 80 kilometers. The spacecraft was
hauled aboard the U.S.S. Okinawa to complete its 10-hour
mission.37

On 9 April 1968, a NASA news release declared that preliminary data on
Apollo 6 indicated that the spacecraft had done its job
well. Mueller and Phillips, however, concluded that the overall flight
had not been a success.

Apollo was not top international or even national news in April 1968,
even though this flight was a major step in the program to land men on
the moon. President Johnson had announced 31 March that he did not
intend to seek reelection, hoping that this action would expedite the
ending of the war in Southeast Asia. And on 4 April, the day of the
flight, Martin Luther King, Jr., a civil rights leader of international
stature, was assassinated in Memphis, Tennessee. About the only
explaining that NASA had to do, therefore, was to the congressional
committees on space activities, who seemed satisfied with what they
heard.38

But the Apollo team did not need a round of public criticism in April
1968. With the decade nearing its end, pressures were already
exceedingly heavy. In the alphabet game of reaching the "G"
(or lunar landing) mission, NASA had flown only two "A"
missions (Saturn V unmanned) and one "B" (Saturn IB with an
unmanned lunar module). Now Huntsville had to find out why the Saturn
V's S-IC first stage bounced, why the S-II second stage turned off two
of its engines, and why the S-IVB third stage refused to fire a second
time. Meanwhile, Houston had to determine exactly how much shaking the
lander could stand and why a large piece of the spacecraft-lunar module
adapter had blown out during launch. Without satisfactory answers, the
Saturn V might have to make a third unmanned flight.

* During Apollo 6 activities, a
small intercenter irritation surfaced. Although almost everyone referred
to the whole Florida launch layout as "the Cape," Albert
Siepert, Deputy Director for Kennedy Space Center Management, wrote
Wesley Hjornevik in Houston to point out that Launch Complex 39 was
situated entirely within the geographical boundaries of the entity known
as the "Kennedy Space Center, NASA." Noting that the
widespread use of "the Cape" was a nostalgic hearkening back
to Mercury and Cape Canaveral, Siepert nevertheless maintained that
"NASA report writers ought not to confuse geographic proximity to
the Cape as the same thing as being on it." However that may have
been, the terminology "launched from the Cape . . ." continued
to be used by the news media - and the present authors.

** The camera photographed sections
of the United States, the Atlantic Ocean, Africa, and the western
Pacific Ocean. This camera had a haze-penetrating film and filter
combination that provided better color balance and higher resolution
than any photographs obtained during the Mercury and Gemini flights.

*** If the S-IVB had made its second
burn, the service module engine would have fired for only 280 seconds.